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This CL also adds unit tests for .foo preloading and updates two tests
that were using http://foo as a test URL.

There are still other places in the code that use http[s]://foo as a test
domain. If this change causes issues for them down the line, they should be
changed to use foo.test or another domain under a test TLD:
https://tools.ietf.org/html/rfc2606#section-2

BUG=b/65158868 (Google-internal)

Change-Id: I8005a3767677e819b8df898ccc073cf1db523d60
Reviewed-on: https://chromium-review.googlesource.com/669396Reviewed-by: Chris Bentzel <cbentzel@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Lucas Garron <lgarron@chromium.org>
Commit-Queue: Lucas Garron <lgarron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#502948}